A mechanical transmission device for modifying torque and speed of rotation from torque input to torque output, more particularly a device capable of modifying torque and speed of rotation in a continuously-variable fashion utilizing a set of levers that are unidirectionally rotatable about a first axis, in conjunction with an abaxial ring rotatable about a second axis, the second axis being itself rotatable about the first axis.
To expand the usefulness of rotary power sources, a variety of torque transmission and conversion devices have been developed. Of particular relevance to the device of this application are situations where it is desirable to greatly reduce the rotational speed of a power source in order to shift it into a useable range; where it is desirable to greatly increase the torque of the power source, whatever the speed; and/or where it is desirable to be able to vary the ratio between input and output rotational speed and torque.
Among the most energy-efficient variable transmission systems are the incrementally shiftable systems that employ multiple gears or chains and cogs, but these systems generally require an interruption in power during shifts, sometimes further requiring supplemental clutch devices and gear synchronizers, and where many ratios are required they can become complex, bulky, and difficult to manage. Continuously variable transmissions offer greater versatility and simplify shifting operations, but have tended to have shortcomings of their own which have limited their usefulness.
The hydraulic or electromotive drives, where a motor drives a pump or generator which then powers another motor, are among the most versatile continuously-variable drives. But they are typically massive and not very energy-efficient, so their use has mostly been restricted to heavy industry and high-load work and transport machinery. Also fluid and electricity is subject to leakage, and can behave as a compressible link, so hydraulic and electromotive drives tend to work poorly with low-speed power sources and the ratios between rotational input and rotational output can be unstable, varying with the load.
Limited-slip differential drives employ a split in the torque path with a brake or clutch or something to provide variable drag to select between paths having different ratios. Energy efficiency can be good when either path is fully selected, but there are frictional losses in all intermediate positions and the intermediate ratios tend to be unstable because the constancy of a given ratio is only as good as the proportionality between the friction and the power load.
Traction drivesxe2x80x94where a ring, disk, or belt frictionally engages a disk, cone, or sphere at varying radiixe2x80x94have stable ratios throughout their range and are often more energy-efficient than limited-slip drives in the intermediate ratios, but the power is transmitted through a rolling frictional interface. This interface can slip if the shear load from the power exceeds the frictional grip, and it tends to be a focal point for polish, wear, heat buildup, and energy-loss problems.
Among the most efficient of the gear reduction drives are the planetary drives, in which a sun gear drives planetary gears within a ring gear, and where large reductions are desired, multiple stages are ganged together in series. Also reasonably efficient are the harmonic drives in which gears with nearly the same number of teeth are made to mesh either indirectly through rolling index gears traveling around the anchor and output gears or directly by physical deformation of one of the gears by rollers or such. Harmonic drives can achieve great speed reductions in a single stage, typically advancing the output gear only one or two teeth per revolution of the index gears or deformation rollers, but there is much sliding action between the teeth of harmonic drives and they often have flexible components in the load path, so they are poorly suited to high-load applications. Also, both planetary and harmonic drive systems have stable ratios, but they are fixed ratios which cannot be varied, so if multiple ratios are needed, multiple gearsets and changing mechanisms are also needed.
Worm drives are also effective speed reducers, but there is much friction in the interface between the screw and the gear it enmeshes, the output torque is both displaced from and not parallel to the input torque, and the reduction ratio of such drives is not variable.
Potentially some of the most energy-efficient of the continuously variable drives are the oscillation drives, where rotary power is converted to oscillating power and then back again to rotary power, and variable gearing is achieved by varying the amplitude of the oscillations. To have continuous power transmission, there must be at least two oscillating elements, each to take the load while the other is returning. Also, oscillation drives have tended to be not very compact. However, oscillation drives have reasonably stable ratios and they can entirely eliminate the frictional rolling interfaces that traction drives require, so the efficiency and durability can be quite good. The main design challenges of the oscillation drives have been to have the oscillating elements receive and deliver power as tangentially as possible to the rotary elements, and to have the input to output ratios remain highly consistent throughout each cycle, while keeping the total number of elements as few as possible.
The device of this application is a transmission with some, but not all, of the properties of a typical oscillation drive. As with many oscillation drives, rotary power an be supplied in either direction in order to produce output power in a single direction. Unlike with most oscillation drives however, true reciprocal motion in the various parts has been replaced with eccentric and intermittent rotary motion.
The objects of the transmission device here disclosed include a reasonably compact gear reduction transmission of simple, yet versatile, design which does not require exotic materials or manufacturing processes to build; having output torque that is co-axial with the input torque, in a ratio which can be steplessly varied from modest reduction to indefinitely high reduction without any interruption of power; including an integral neutral for zero transmission of power; operating with low friction so as to minimize wear, heat buildup, and power-loss problems; adaptable to high and low load applications; capable of utilizing slow or fast power sources that are either unidirectional or bidirectional in nature; and easily adaptable to provide unidirectional or bidirectional torque output.
Accordingly, this transmission device is thought to have numerous advantages over existing gear reduction systems. This device can match the continuous variability of hydraulic and electromotive transmissions, but unlike with those systems, any selected ratio will be quite stable independent of load, it should have better energy efficiency, and the effectiveness will not diminish even with power sources that have extremely slow rates of rotation. This device can match or exceed the variability of traction drives, but is not dependent upon a rolling frictional interface to transmit torque, so it should be able to handle higher loads without the slippage, heating, and wear problems. This device compares well against the efficiency and ratio stability of planetary, harmonic, and worm drives, but unlike those drives, the ratio between input and output rotation can be steplessly varied over a large range; it does not require multiple stages in series to achieve great gear reductions; and when compared to flexible harmonic drive systems, this should be more suitable for high-load situations.
A transmission with such properties can have applications in diverse areas including gear reductions for electrical motors, turbines, or other high speed rotary power sources where it is desirable to reduce the speed of rotation and have the output speed variable, for example so that the power source can operate at an optimal speed. It could also have application with variable-speed power sources, such as large flywheels, where it is desirable to have a consistent output speed. It could also have utility in compact, low-speed, high-load, rotary or angular applications for portable or battery-powered equipment, such as winches, pincers, prisers, augers, bolt drivers and such, or larger high-load applications such as skid-steer and heavy machinery transmissions, conveyance equipment, turret rotators, flywheel accelerators, centrifugal extractors, or transporters wherein loads must be smoothly accelerated or where great torque is sometimes desirable, but other times less torque and more speed is preferablexe2x80x94especially where a smooth transition between these two states is advantageous. And an application is also seen in hybrid machines, such as electric-assist bicycles, where there is a large mismatch in the optimal operating speeds of two power sources which have to work in conjunction with one another, and particularly if both will need to accommodate a wide range of loads and output speeds. Further objects, advantages, and applications will become apparent from a consideration of the ensuing description and accompanying figures.
Applicant""s invention employs a rotating torque-input element rotating on a primary axis (the primary axis being an arbitrary reference axis which may be coincident with the axis of a wheel, pulley, crank, gear, or any other rotatable element for delivering or receiving torque); an abaxial element rotating on a secondary axis parallel to, but typically not coincident with, the primary axis; a linkage between the torque element and the secondary axis by which rotation of the torque-input element will urge the secondary axis of the abaxial element to orbit the primary axis; a rotating torque-output element rotatable upon the primary axis; a multiplicity of levers radiating from the primary axis, each rotatable upon the primary axis; devices for sometimes holding each lever unrotatable; devices for engaging each lever with the torque-output element; and lever engagement devices arranged around the abaxial element for engaging the abaxial element with the multiplicity of rotatable levers such that, for each lever, a given point on the abaxial element will lie upon a given radial axis of that lever.
The torque-input element can bear torque directly along the primary axis, such as through an axle, or it can bear torque indirectly from a surrounding housing rotatable upon the primary axis, but an advantage in terms of simplicity is seen in having the torque-input element take the form of a rotatable axle, and this we may call the drive axle. The torque-output engagement devices can engage the levers to the torque-output element at any radius, but since the load on such devices would decrease as the radius increases, an advantage is seen in locating these devices at the far end of the levers, away from the axis of rotation. The torque-output engagement devices can take many forms, but the simplest will tend to be clutch devices which engage and disengage automatically according to the relative motion between the lever and the torque-output element. Because these clutches will be operating at some distance from the primary axis, the torque-output element will tend to be ring-shaped, as in a section of cylinder, cone, or disk, and may thus be referred to as the torque-output ring. There are a variety of ways in which to hold each lever sometimes fixed, but an advantage in economy and versatility is seen in having a structure similar to the torque-output ring, also centered on the primary axis, except having this ring non-rotatable. This may be called the fixed ring, and clutches like the torque-output clutches can sometimes engage each lever to the fixed ring. The abaxial element carrying the lever engagement devices can assume a variety of shapes but for compactness and simplicity of the bearing interface, a ring shape is again generally advantageous, and thus may be referred to as the abaxial ring. There can be a variety of devices for engaging the abaxial ring to each lever such that a given point on the ring lies on a given radial axis of that lever, but one of the simplest would be a stud affixed to the abaxial ring slidably mounted within a radial slot in the lever, and so the lever engagement devices of the abaxial ring may be called abaxial ring studs.
Using these terms, and with reference to the enclosed figures, the operating principle of this device can be described generally in terms of a preferred embodiment. It is seen that the transmission device has a drive axle rotating on a first axis, and a carriage affixed to the axle carrying a ring, namely the abaxial ring, rotating on a second axis such that the second axis rotates with the axle about the first axis. The transmission has a ring which can rotate about the first axis for torque output, and a ring which is fixed but centered on the first axis. It has a set of levers rotatable about the first axis, each lever capable of limited rotation independent of the other levers, and each lever typically has at least two clutchesxe2x80x94one to hold it non-rotatable (fixed ring engagement) and the other for torque output (driven ring engagement). Studs are arranged around the abaxial ring, and these studs operate within radially oriented slots within the levers. Radial motion of a stud will cause it to travel along and within its slot, and tangential motion of the stud will cause it to bear against the walls of its slot and impart rotational force to the corresponding lever.
The operation can be summarized as follows. The drive axle is connected by a gear, pulley wheel, or such to a power source. When the drive axle is made to rotate, it urges the secondary axis of the abaxial ring around the axis of the axle. The twist of the axle applies force at the second axis in a direction tangential to its orbit at any given time. Abaxial ring studs which are most in line with this tangent will tend to travel largely in line with the radial axis of their respective levers, and thus will tend to travel in their respective slots imparting little rotation to those levers. Abaxial ring studs which are most perpendicular to this tangent will tend to travel in a direction largely perpendicular to the radial axis of their levers and thus will tend to rotate those levers and will have little travel within their respective slots. The studs most perpendicular to this tangent will lie on opposite sides of the axle, and so will tend to rotate their respective levers in opposite directions about the axle. However, each lever has a clutch which can engage the fixed ring, which clutches collectively operate to ensure that all levers can only rotate in one direction, so the studs most perpendicular to the tangent of the orbit will urge at least one lever on one side of the primary axis against the direction of its fixed-ring clutch and will thus hold it anchored to the fixed ring, but levers on the other side of the primary axis will be urged to rotate in a direction their fixed-ring clutches will allow, and will be free to rotate in that direction. Each lever also has a clutch which engages the torque-output ring, and each torque-output clutch is similarly oriented and configured to ensure that the torque-output ring will rotate in the same direction as each lever and no slower than each lever. Thus where any levers are made to rotate, the torque-output ring clutches ensure that the torque-output ring rotates no slower than the fastest rotating lever, and this will be the lever that drives the torque-output ring. Each lever will, in succession, alternately function as fixed lever and torque-output lever, with an unloaded phase between each state, as the abaxial carriage orbits the primary axis.
The load path is from the drive axle, to the secondary axis, then to the abaxial ring in a direction tangential to the orbit of the secondary axis, then to a lever which cannot rotate as well as to a lever which can rotate, causing the rotation of the rotatable lever, and then out the torque-out clutch on that lever to the torque-out ring. Power is conveyed from the axle to the abaxial ring purely tangentially to the orbit of the abaxial axis. Power is conveyed between the abaxial ring and the levers perpendicularly or nearly so to the radial slot walls. Power is conveyed from the fastest lever to the driven ring purely tangentially to the driven ring rotation. Friction losses between the clutches and rings and between the levers and studs should be minimal. The principle energy losses will most likely be flex losses and normal bearing losses at the abaxial ring and at the center of lever rotation.
If the distance between the axis of the abaxial ring and the axis of the axle is decreased, the force applied at the abaxial ring axis will increase and the tangential velocity will correspondingly decrease if the rotational speed of the drive axle is held constant, so reducing the distance between the first and second axes decreases the speed and increases the torque at the torque-output ring. When the distance between the axis of the abaxial ring and the axis of the axle reaches zero, tangential motion at the abaxial ring axis also reaches zero, and the axle spins freely with no transmission of power. There is a dissymmetry between matching and non-matching directions of rotation between the axle and the torque-output ring, resulting in different amounts of gear reduction, and this attribute of the transmission""s operation will be examined in greater detail shortly, with the assistance of FIG. 5.